Rotary drill bits and cutters



Jan. 26, 1960 A. w. KAMMERER 2,922,627

ROTARY DRILL BITS AND CUTTERS Filed June 7, 1956 2 Sheets-Sheet 1 IN VEN TOR.

4966396,? "(KIA/M47666 Jan. 26, 1960 A. w. KAMMERER ROTARY DRILL BITS AND CUTTERS 2 Sheets-Sheet 2 Filed June 7, 1956 R m H W.

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ROTARY DRILL BITS AND CUTTERS Application June 7, 1956, Serial No. 589,987

Claims. "(CL 25576) The present invention relates to drilling tools, and more particularly to tools usable in a well bore to perform diverse operations therein, such as milling out a portion of casing in the well bore.

Rotary drill bits of the expansible type are used to sever and mill away a desired extent or length of easing disposed in a well bore. Such bits include cutters disposed initially in retracted position, which are expanded outwardly to sever the casing at a predetermined point, after which the expanded cutters are effective to drill ahead on the casing as the bit is rotated and gradually lowered in the well bore.

The cutters have hardfacing material, such as tungsten carbide, deposited on their various cutting faces or surfaces, the hardfacing material being bonded to the body portions of the cutters, which are usually made of steel. After the cutters have been expanded to sever the casing, appropriate drilling weight is imposed thereon through the agency of the drill string to which the tool is secured, to cause the cutters to mill away the well casing. As the casing milling operation proceeds the casing erodes the cutters. The cutter body metal, being softer than the hardfacing material, tends to erode more readily than the latter, which is desirable since it results in a slight projection of the hardfacing ahead-of the body metal, placing the hardfacing in position to operate on the casing in a relatively unimpeded manner.

Despite the desirability of having the body metal erode or be worn away more readily than the hardfacing, this action may not occur, the body metal riding along the severed top of the casing and preventing the hardfacing material from engaging the upper end of the casing with sufficient cutting force.

Accordingly, it is an object of the present invention to insure the wearing away of the cutter body metal in advance of the adjacent hardfacing material, so that the latter can have effective engaging or cutting force against the well casing, or other substance on which it is operating.

Another object of the invention is to provide a cutter capable of drilling well casing or other substances in the well bore, in which the cutter body metal will wear away before the adjacent hardfacing material erodes to the same extent, and in which the cutter blade is of strong and sturdy construction to withstand safely the loads encountered in the well bore.

A further object of the invention is to provide a rotary drill bit having a relatively large number of cutter teeth for milling away casing in the well bore, or for drilling away other substances in the well bore, in which a greater clearance between adjacent teeth is provided, for the same number of cutter teeth, to enhance the removal of chips or other cuttings from between the teeth, which is particularly desirable in relatively small size bits.

An additional object of the invention is to provide a rotary drill bit in which the cutter teeth are so shaped as to permit a greater number of cutter teeth to be incorporated in the bit, particularly in relatively small sizes,

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' through which chips or other cuttings can be moved during the drilling operation.

Yet another object of the invention is to provide a rotary drill bit having cutter teeth arranged adjacent one another, which are shaped to provide greater clearance between adjacent teeth, thereby making it easier to apply hardfacing to the teeth.

Still a further object of the invention is to provide a rotary drill bit having cutter teeth or a cutter tooth shaped to permit application of a greater amount of hardfacing to the cutting faces or face thereof, thereby increasing.

the drilling life of each tooth.

This invention possesses many other advantages, and has other objects which maybe made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in thedrawings accompanying and forming part of the present specification. These forms will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such de-- tailed description is not to be taken in a limiting sense,.

since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a longitudinal section through an embodiment of the invention disposed in a well casing, with the cutters and other parts occupying their initial retracted positions;

Fig. 2 is a longitudinal section similar to Fig. 1, disclosing the cutters locked in their fully expanded position; I

Fig. 3 is an enlarged view of a cutteracting upon the upper severed end of a casing section; I

Fig. 4 is an inner side elevation of the lower part of one of the cutter structures;

Fig. 5 is a bottom plan view seen along the line 55 on Fig. 3;

Fig- 6 is a cross-section of a cutter tooth as seen along the line 66 on Fig. 3;

Fig. 7 is a longitudinal section through another form of cutter tooth structure;

Fig.- 8 is a cross-section taken along the line 88 on Fig. 7; i

Fig. 9 is a bottom plan view of another embodiment of cutter structure;

Fig. 10 is a bottom plan view of still a further embodiment of a cutter tooth structure.

As shown in the drawings, a rotary expansible drill bit or milling tool A is secured to the lower end of a string of drill pipeB that extends to the top of the well bore C, and by means of which the drill bit is lowered through a string of well casing D to a region therein Where a casing milling operation is to commence. Although described herein in connection with a casing milling operation, it is to be understood that the apparatus is capable of performing other operations in the well bore, such as enlarging its diameter.

The upper portion of the rotary drill bit consists of a mandrel 10 having an upper pin 11 threadedly connected to the .lower end of the string of drill pipe B. This mandrel includes an upper kelly or drill stem member 12 slidably splined to the main body 13 of the drill bit. The exterior of the lower portion 14 of the kelly is non circular in shape, being telescopically received in a companion non-circular socket 15 formed in the main bit body 13. Specifically, the kelly exterior and the socket 15 may be of hexagonal shape, to enable the kelly 12 to be moved longitudinally with respect to the body 13, while still being capable of transmitting rotary motion to the body.

The mandrel 10 has a limited range of longitudinal Patented Jan. 26, 1960 movement within the body, its downward movement being determined by engagement of the lower end 16 of the kelly with an inwardly directed body shoulder 17, and its upward movement being limited by engagement of an external shoulder or piston portion 18 of the kelly 'with a cylinder head '19 secured to the body. The upper end of the head has a flange 20 engaging a body shoulder 21, the flange being prevented from moving upwardly of the body by split snap retainer rings 22 fitting in a body groove 23 and overlying the flange 20. An annular guide 24 is releasably secured to the body 13 by a split snap ring 25 above the retainer rings.

The body 13 has a plurality of expansible parts mounted on it. These include cutter supporting members 26 pivotally mounted on body slots 27 on hinge pins 28 and suitably secured to the body to prevent their losstherefrom. Each cutter supporting member 26 depends from the hinge pin 28 and carries a drag or milling cutter structure 29 at its lower end, which structure is specifically described hereinbelow.

The cutter supporting members 26 and the cutter structures 29 themselves tend to occupy a retracted position substantially entirely within the confines of the main body 13 of the bit. These cutter supporting members and the cutter structures are expandible outwardly, to sever the casing and mill it away by operating upon the upper end E of the casing therebelow. To accomplish the expansion, each cutter supporting member 26 has an inclined expander surface 3i? on its inner portion below the hinge pin 28 which tapers in a downward and inward direction. Each expanded'surface terminates in a lock surface 31 formed on a lock portion 32 of the cutter supporting member. The outward expansion is accomplished by producing relative longitudinal movement between the mandrel 19 and the bit body 13, which will-produce relative longitudinal movement between the cutter supporting members 26 and the tubular member 33 of the mandrel 10. This tubular member includes a lower portion 34 slidable within a guide bushing 35 mounted in a bridge 36 secured to the body and extending across the body slots 27'. This guide bushing 35 is disposed below the lock portions 32 of the cutter supporting members 26.

Located initially substantially above the guide bushing 35 and below the hinge pins 23, and in cutter member recesses 37, is a mandrel lock and expander 38 which has outer surfaces 39 adapted to engagethe expander surfaces 30 and the lock surfaces 31. The lock and expander 38 may be formed integral with the tubular member 33, the upper end of the latter being piloted within a socket 49 formed in the lower portion 14 of the kelly 12. An enlarged boss 41 on the tubular member 33 engages a downwardly facing shoulder 42 of the kelly, the tubular member being held against this shoulder by a suitable split retainer or lock ring 43 snapped into an internal groove 44 encompassing the kelly socket and engagin the lower end of the tubular member boss 41.

Drilling mud or other fluid can pass down through the central passage 45 in the kelly or drill stem 12 and into the central passage 46 extending completely through the tubular member 33. Leakage of fluid around the exterior of the tubular member 33 is prevented by a suitable side seal ring 47, such as a rubber O ring, .in a peripheral grve'48 in the kelly, which engages the interior of the boss 41.

Assuming that the body 13 of the tool is elevated relatively along the tubular mandrel 10, the inclined expander surfaces 30 of the cutter supporting members 26 will be shifted upwardly along the lock and expander portion 38 of the tubular member 33. During such upward shifting, the cutter supporting members 26, and the cutter structures 29 carried thereby, will be pivoted about the tubular mandrel 10 can continue until the cutter structures 29 have been shifted outwardly to their fullest extent, as determined by engagement of stop shoulders 49 on the cutter supporting members 26 with companion shoulders formed in the body on opposite sides of the body slots 27. When such engagement occurs, the lower end 16 of the kelly portion 12 of the tubular mandrel will engage the body shoulder 17, and the lock degrees apart from each other.

the hinge pins 28 and urged in an outward direction.

The upwardmovement of the body '13 with'res'pectto and expander 38 on the tubular member 33 will be disposed behind and in engagement with the lock portions 32 on the cutter supporting members 26 (Fig. 2).

It is to be noted that the surfaces 31 of the lock portions 32 of the cutter supporting'members 26 and the companion surfaces 39 on the lock and expander portion 38 of the tubular member are substantially parallel to the axis of the drill bit, to prevent the reactive forces on the cutter structures 29 from moving the latter inwardly. As a practical matter, it is preferred that the coengaging lock surfaces 39, 31 be inclined slightly in a downward direction toward the axis of the tool, to insure release of the lock and the expander portion 38 from the cutter supporting members 26 when the latter and the cutter structures 29 are to be shifted to retracted position.

The relative longitudinal movement between the tubular mandrel 10 and the body 13 of the tool is accomplished hydraulically in the specific form of apparatus disclosed in the drawings. Thus, the piston or enlarged portion 18 on the drill stem 12 is received within a counterbore 51 formed on the upper portion of the body of the tool. This upperpor-tion actually constitutes a cylinder 52 having a cylindrical wall 53 extending from a lower shoulder 54, defining the bottom of the counterbore51, to the cylinder head 19.

A confined cylinder space 55 is formed between the piston'portion 18 of the kelly, the periphery of the kelly above the piston, and the cylinder 52. A suitable packing or side seal ring 56 may be disposed in a suitable piston ring groove 57 formed in the piston 18, which is adapted to slidably seal against the cylindrical wall 53 of the cylinder 52. Fluid is thereby prevented from passing in a downward direction between the piston and the cylinder. Similarly, fluid is prevented from passing in an upward direction out of the annular cylinder space 55 by an inner side seal ring 58 carried in an internal groove 59 in the cylinder head 19 and slidably and sealingly engaging the periphery of the kelly 12 above the piston 18, and also'by an outer side seal ring 60 disposed in an external groove 61 in the head 19 and sealingly engaging the cylinder wall 53.

Fluid under pressure in the string of drill pipe B and in the tubular mandrel passage 45 can be fed into the cylinder space 55 through one or more side ports 62 establishing communication between the central passage 45 through the kelly and the cylinder space. Such fluid under pressure is developed, in the form of invention'disclosed in the drawings, by virtue of the fact that the passage 46 through the tubular member 33 of the mandrel 10 is of a restricted diameter as compared to the passage 45 through the kelly portion of the mandrel. As a result, the pumping of drilling mud, or other fluid, at an adequate rate through the apparatus will build up a back pressure of fluid in the passage 45, which pressure will be imposed on the fluid in the cylinder space 55, acting upon the cylinder head 19 to urge the body 1.3 of the tool in an upward direction with respect to the tubular mandrel 1Q, to secure the outward expansion of the cutter supporting member 26 and cutter structures 29 to their fullest extent, as above described.

As apparently disclosed in the drawings, a set of di-- ametrically opposed supporting members 26 and cutter structures 29 are employed, displaced substantially 180 Actually, it is preferred tofem'ploy three sets of supporting members and supporting structures displaced substantially degrees from each other, to secure a smoothly running rotary expansible bit. The two sets of supporting member structures are shown in the interests of simplicity of the drawings. Each cutter structure 29 is secured to the lower portion of a cutter supporting member 26 by use of welding material 70, which functionally integrates the cutter structure to the depending supporting member or leg 26. The lower portion of the cutter structure preferably has a plurality of depending legs 71, 72, 73 separated from one another by substantial spaces 74,the depending legs, in effect, constituting cutter teeth, which depend to substantially the same extent from the upper body portion 75 of the cutter structure. The lower ends of the teeth 71, 72, 73 are preferably provided with hardfacing material 76, whereas the leading faces of the depending teeth are also provided with hardfacing material 77. Such hardfacing material may be of any suitable type. However, it is found that the brazing of sintered tungsten carbide particles on the leading faces of the teeth, as well as on their bottom faces or surfaces, is very effective in milling away casing sections and in acting upon very hard formations.

As specifically disclosed in the drawings, each cutter structure 29 has three depending legs or teeth 71, 72, 73, although the number can be varied. it is preferred to use a plurality of teeth, in order to have a large cutting surface in contact with the casing section or formation, after the cutter supporting members 26 and cutter structures 29 have been expanded outwardly to their maximum extent. The necessary drilling weight can be imposed on the string of drill pipe B and on the rotary drill bit A itself, to secure a proper cutting away of the casing material or of the formation. However desirable the plurality of teeth may be, they offer a disadvantage in securing the initial severing cut in the casing D in view of the large surface that will contact the inner wall of the casing and the relatively limited expanding force available for urging the cutters 29 from their retracted to their fully expanded positions.

The aforenoted disadvantage is overcome by causing a lesser number of teeth to engage the casing D and make the severing cut than are available to engage the casing at E after it has been severed, and when drilling weight can be imposed in a downward direction on the cutters 29. Thus, it will be noted that each cutter tooth '71, 72, 73 extends radially outward beyond the upper body portion 75 of the cutter structure 29, but that only some of the cutter teeth, such as the end teeth 71, 73, are capable of engaging the casing in effecting its severing. As specifically disclosed, the end teeth 71, 73 are each provided with a layer of hardfacing material 78 running lengthwise therealong from the lower end of the tooth to the region where the tooth emerges into the body portion 75 of the cutter structure, and that such hardfacing material 78 extends radially outward of the cutter structure to a much greater extent than the intermediate tooth 72. As a matter of fact, since the intermediate tooth 72 is not caused to perform any severing action on the casing D, it is not even supplied with hardfacing material on its outer surface 72a. Its outer surface is disposed inwardly of the outer hardfaced surfaces 78a of the end teeth 71, 73 to a substantial extent, so that the outer face of the intermediate tooth cannot even engage the casing until the end teeth 71, 73 have completed the severing action on the casing.

The lower ends of the teeth will all lie substantially in the same plane when the cutter supporting members 26 and cutter structures 29 have been expanded outwardly to their maximum extent, whereas the outer surfaces 78a of the end teeth 71, '73 lie on an arc of a circle that has a substantially greater radius than the arc of the circle on which the outer surface 72a of the intermediate tooth lies.

In the operation of the apparatus A, it is run in the Well casing with the cutter supporting members 26 and the cutter structures 29 in their initial retracted position, such as shown in Fig. l. The lower portion of the body 13 of the apparatus may have a pilot structure secured thereto, such pilot structure being constituted by circumferentially spaced, longitudinally extending blades 81 which are capable of riding along the wall of the casing D, to center the apparatus therewithin. When the apparatus has been lowered to the desired point in the well casing D at which the latter is to be severed, the pumps at the top of the Well bore are started to pump fiuid at a sufiicient rate through the drill pipe B and into the mandrel passages 45, 46, building up a back pressure in the kelly passage 45 and in the fluid in the ports 62 and cylinder space 55, which pressure will act upon the cylinder head 19 to urge the body 13, the cutter supporting members 26, and the cutter structures 29 in an upward direction with respect to the mandrel 10.

During such upward movement, the expander surfaces 363 on the cutter supporting members 29 are brought to bear against the lock and expander portion 38 of the mandrel, the cutter structures being urged in an outward direction against the wall of the well casing. The drill pipe B and the rotary drill bit A are rotated at proper speeds while fluid is being pumped through the apparatus, the outer casing severing or reaming edges 78 of the cutter teeth 71, 73 acting upon the wall of the casing and gradually milling it away. During this operation, the apparatus is retained in the same longitudinal position in the well casing. As the casing is cut away, the hydraulic force acting upon the body 13 raises it and the cutter supporting members 26 and cutter structures 29 to a further extent, until the reamer edges 78 of the cutter teeth 71, 73 have completely severed the casing. Such severing action will occur before the outer face 72a of the intermediate cutter tooth 72 can engage the inner wall of the casing D. Thereafter, rotation of the drill pipe B and the rotary drill bit A continues, so that the reamer edges 78 continue to cut away the casing and dig into the formation, until the cutters 29 have been fully expanded outwardly to the maximum extent, as determined by engagement of the stop shoulders 49, 50, and the lower end 16 of the kelly portion of the mandrel with the body shoulder 17. With the parts in this position, the lock portion 32 of the cutter supporting member 26 will bear against the lock and expander portion 38 of the tubular member 33 to preclude inadvertent partial retraction of the cutter structures 29 from their fully expanded position.

Downweight of the proper amount is now imposed on the string of drill pipe B, this downweight being transmitted through the kelly '12 to the body shoulder 17, and from the body through the stop shoulders 50, 49 directly to the supporting members 26 and the cutter structures 29, urging the three blades 71, 72, 73 of each cutter 29 against the upwardly facing severed end B of the well casing D. It is evident that a greater number of teeth and surfaces are now available for a milling action upon the upper end E of the casing than was used in severing the casing. Assuming that three sets of supporting members 26 and cutter structures 29 are used, each cutter structure 29 having the configuration disclosed in Fig. 4, a total of nine cutter teeth will be available for action upon the severed end E of the casing.

With such large number of cutter teeth, and in view of the extent of their bottom faces 76, a relatively large drilling weight can be imposed upon the cutter teeth to cause a relative rapid milling away of the casing D. The drilling weight can be varied within wide ranges. However, since the expanding force in making the severing cut on the casing is limited to the hydraulic pressure that can be made available in the cylinder space 55, and since the total force, as a practical matter, can only be of a certain maximum value, the distribution of the outward expanding force over a lesser number of teeth 71, 73 than are used in milling away the casing after it has been severed, means that a greater unit penetrating pressure is being supplied on the reamer edges 78 of the teeth 71, 73*than would be present if the intermediate tooth 72 were .also made effective in performing the casing severing action. With such latter tooth '72 active, inadequate penetration into the casing wall might result.

It is to be noted that the cutter blade structure 29 includes the body metal 71, 72., 73, usually made of a proper grade of steel, with the hardfacing material 76, 77, 78 applied to its various cutting faces, such as its forward face 85, the bottom face 86, and at least some of the reaming faces 87 of each cutter blade or tooth. After the cutters 29' have been expanded outwardly to their fullest extent and are operating upon the upper severed end E of the well casing, the cutters are subjected to the proper drilling weight, this weight causing the hardfacing 76, 77 to engage the upper end of the casing and reduce it to the form of chips as the tool is rotated. T he hardfacing 76 at the bottom of the tool will eventually Wear or be broken away as the drilling action occurs, whereupon the body metal 71, 72, '73 behind the hardfacing material 77 on the forward or leading face is effective to operate upon the severed end E of the well casing, the lower surface of the body metal itself also engaging and riding upon the upper end E of the severed well casing.

Heretofore, the area of contact of the steel body portion of the blades engaging the upper end of the casing has been comparatively large, the drilling weight being distributed over a large area of such lower body surfaces, which retarded the rate of wear of such surfaces. It is desirable for the body metal to wear or erode more readily than the hardfacing material 77, in order that the hardfacing material can engage the severed end of the casing with proper force imposed by the drilling weight on the tool, to secure the cutting action on the casing and its reduction to chips or particles that are flushed away by the drilling fluid. By virtue of the present invention, a strong cutter tooth or cutter blade construction is provided having a long life, and in which the area of the body metal engaging the severed upper end B of the casing is diminished considerably, without diminishing the hardfacing available for cutting action upon the casing.

In the form of the invention disclosed most clearly in Fig. 5, the casing D is disclosed in broken lines in the position that it occupies with respect to a cutter structure 29 after the latter has been expanded outwardly to its maximum extent. The leading face 85 of the body metal portion of each tooth is formed in concave fashion, whereas the trailing face 88 may he comparatively straight, as illustrated in Pig. 5. The hardfacing material 77 on the leading face may also have a uniform thickness and will present the concave leading surface 89 disclosed in Fig. 5. By making the leading surface 35 of the body metal concave, the area of the bottom part of the steel body portion of each tooth is decreased substantially, as compared with the making of the leading face straight, which was done heretofore. Accordingly, the area of contact of the body portion of each cutter tooth upon the severed end of the casing is much less, so that the unit force of the bottom portion of each cutter tooth acting upon the casing is increased, which will produce an increased Wearing away of the body metal and insure the exposure and availability of hardfacing '77 for action upon the severed upper end E of the well casing D. In Fig. 5, the position of the leading face of the body metal, if it were made straight across, is disclosed in broken lines 85a, showing quite clearly the decreased area of contact of the body metal upon the severed upper end of the well casing D that results from making the leading face 85 concave.

The making of the leading face 85 concave has a further advantage than insuring proper penetration of the hardfacing 77 against the upper end of the well casing. Such concavity provides a much greater clearance space 74 between adjacent teeth 71, 72 and 72, 73 through which the chips or cuttings produced by the teeth can be flushed by the drilling fluid circulated down through the drill pipe and through the tool, this fluid discharging from a lower end of a mandrel passage 46 and then passing outwardly between the cutter teeth. The circulating fluid not only maintains the tooth faces 89 free from chips or cuttings, but insures that the teeth remain in a cool condition, which enhances their useful life.

Instead of the forward faces of the body portion of each cutter tooth being made concave in order to decrease the area of contact of each tooth with the upper end of the severed well casing, the same results can be achieved by making the trailing faces or surfaces 8821 of the body of each tooth concave, such as disclosed in Fig. 9. As shown herein, the leading faces 35b can be made straight and they may also have a uniform thickness of hardfacing material 77, such as tungsten carbide applied thereto. The trailing face 88a of each tooth body is concave, as shown, which will have the effect of decreasing the area of each tooth body engaging the severed end E of the well casing, insuring its erosion or wearing away at the proper rate to secure effective cutting engagement of the hardfacing material 77 with the casing.

The making of the trailing faces 33a in concave fashion, such as disclosed in Pig. 9, also provides increased clearance spaces 74a between adjacent teeth, through which the cuttings can be flushed by the drilling fluid being pumped down through the drill pipe for discharge from the mandrel passages 45, 46.

In the form of cutter structure disclosed in Fig. 10, the leading faces 85 of each tooth body are made concave in the same manner as illustrated in Fig. 5. However, the leading faces 850 of the hardfacing material 77 is made straight across, which permits a larger amount of hardfacing material 77 to be deposited on each tooth, tending to give each tooth a greater cutting life. Here again, the area of the body metal of each tooth in cont act with the upper end E of the severed casing has been decreased to insure its wearing away at the proper rate, tosecure eflective penetration of the hardfacing material 77 against the upper end of the severed casing.

Despite the decreasing of the area of the body metal in each tooth where it contacts the upper end of the severed casing, each tooth is of strong and sturdy construction, inasmuch as its thickness inwardly and outwardly of its location of engagement with the well casing D is considerably greater than its thickness where it engages the well casing. Such thicker portions buttress and support the cutting surfaces of each tooth and prevent its deflection or breaking.

In the form of invention disclosed in Figs. '7 and 8, the body of each tooth has a vertical groove W formed therein at the location of engagement of the cutter tooth with the severed upper end B of the well casing. This vertical groove 9%, which may extend completely through the thickness of the tooth to the proper height, is filled with hardfacing 91. Inasmuch as the operation of the cutters on the well casing causes the casing to wear away a vertical groove in each blade or tooth, the hardfacing 91 in such vertical. groove can act upon the severed casing, providing a much greater hard facing area of contact against the severed end E of the casing, to expedite the milling action. Not only is the milling action expedited, because a much larger surface of hardfacing is available, but the life of each cutter tooth is considerably increased. Instead of the body metal of each tooth engaging and riding upon the severed casing end, substantially none of the body metal so rides on the casing, since the hardfacing material 91 extends through the entire thickness of the cutter tooth or blade.

The making of the leading or trailing face of each cutter tooth concave provides greater clearance 74 or 74a between adjacent teeth, as has been pointed out above. This not only enhances the flushing of chips and other cuttings from the clearance spaces between the teeth, to maintain them free from such undesired materials, but it also gives increased room that facilitates the application of the hardfacing 77 to the leading faces of the cutter teeth themselves. Moreover, such increased clearance space between adjacent teeth makes it possible to provide a greater number of teeth on each cutter structure 29 in the small sizes of tools. Where the use of straight leading and trailing surfaces on each tooth would permit only two teeth to be embodied in a cutter structure, in view of space l-imitations and the necessity to provide adequate clearance between adjacent teeth, the making of the leading or trailing tooth faces concave permits three teeth to be incorporated in a cutter structure. In other words, the number of teeth that can be incorporated in a rotary drill bit in the small sizes has been increased by fifty percent, which should correspondingly increase the effective life of the bit.

Regardless of the form of apparatus and cutter construction that is used therein, when it is desired to retrieve the apparatus from the well bore, as, for example, when the cutter teeth have become worn, or the milling or other operation of the well bore has been completed, it is only necessary to discontinue the pumping of the drilling fluid through the drill pipe B and the apparatus A, to relieve the pressure in the cylinder 52, and elevate the drill pipe. Such elevating movement will elevate the tubular mandrel with respect to the body 13 and the cutter supporting members 26, to raise the lock and expander portion 38 above the expander surfaces 30, whereupon the cutter structures 26, 29 can drop back to their retracted position, such as disclosed in Fig. 1. In the event the cutters are reluctant to move to such position, the outer surfaces 26a of the cutter supporting members 26 will engage the casing above and adjacent the location of the severing out, upon elevation of the apparatus in the well bore, which will force the cutter supporting members 26 inwardly, enabling the apparatus to be withdrawn through the well casing D to the top of the well bore.

The inventor claims:

1. In a rotary drill bit to be lowered in a well bore: a main body; a supporting member mounted on said body for expansion laterally outward of said body; a drag cutter structure secured to said supporting member; means for expanding said member and cutter structure laterally outward of said body; said drag cutter structure having a plurality of depending teeth spaced from each other arcuately with respect to the bit axis and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a substantially greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces; at least one tooth having one of its faces concave in a direction laterally of said one tooth, whereby said one face is spaced different distances from said other face of said one tooth to provide a vari able tooth thickness laterally of said tooth.

2. In a rotary drill bit to be lowered in a wellbore: a main body; a supporting member mounted on said body for expansion laterally outward of said body; a drag cutter structure secured to said supporting member; means for expanding said member and cutter structure laterally outward of said body; said drag cutter structure having a plurality of depending teeth spaced from each other arcu- I ately with respect to the bit axis and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a substantially greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces; each of said teeth having one of its faces concave in a direction laterally of the tooth, whereby said one face is spaced different distances from the other face of the same tooth to provide a variable tooth thickness laterally of the tooth.

3. In a rotary drill bit to be loweredin a well bore:

a main body; a supporting member mounted on said body for expansion laterally outward of said body; a drag cutter structure secured to said supporting member; means for expanding said member and cutter structure laterally outward of said body; said drag cutter structure having a plurality of depending teeth spaced from each other arcuately with respect to the bit axis and having their lower cutter faces lying in the same plane so that all teeth andlower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a substantially greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces; each of said teeth having its leading face concave in a direction laterally of the tooth, whereby said leading and trailing faces of each tooth are spaced different distances from each other to provide a variable tooth thickness laterally of the tooth.

4. In a rotary drill bit to be lowered in a well bore:.

a main body; a supporting member mounted on said body for expansion laterally outward of said body; a drag cutter structure secured to said supporting member; means for expanding said member and cutter structure laterally outward of said body; said drag cutter structure having a plurality of depending teeth spaced from each other arcuately with respect to the bit axis and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a substantially greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces; each of said teeth having its trailing face concave in a direction laterally of the tooth, whereby said leading and trailing faces of each tooth are spaced different distances from each other to provide a variable tooth thickness laterally of the tooth.

5. In a rotary drill bit to be lowered in a well bore: a main body; a supporting member mounted on said body for expansion laterally outward of said body; a drag cutter structure secured to said supporting member; means for expanding said member and cutter structure laterally outward of said body; said drag cutter structure having a plurality of depending teeth spaced from each other arcuately with respect to the bit axis and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a substantially greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces; at least one tooth having an intermediate groove therein extending upwardly from said lower cutter faces; and hard facing material in said groove secured to said one tooth.-

6. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; a drag cutter structure secured to said supporting member; said drag cutter structure including a plurality of depending teeth of extended length spaced from each other arcuately with respect to the bit and axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a longitudinally greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; at least one tooth having one of its faces concave in a direction laterally of said one tooth, whereby said one face is spaced different distances from said other face of said one tooth to provide a variable tooth thickness laterally of said tooth.

7. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting member; said drag cutter structure including a plurality of depending teeth of extended length spaced from each other arcuately with respect to the bit axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a longitudinally greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; each of said teeth having one of its faces concave in a direction laterally of the tooth, whereby said one face is spaced different distances from the other face of the same tooth to provide a variable tooth thickness laterally of the tooth.

8. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; a drag cutter structure secured to said supporting member; said drag cutter structure including a plurality of depending teeth spaced from each other arcuately with respect to the bit axis and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a longitudinally greater extent than the corresponding outer surface of another of said teeth; each of said teeth having aleading and a trailing face; hardfacing material on said leading faces; each of said teeth having its leading face concave in a direction laterally of the tooth, whereby said leading and trailing faces of each tooth are spaced different dis tances from each other to provide a variable tooth thickness laterally of the tooth.

9. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting member; said drag cutter structure including a plurality of depending teeth of extended length spaced from each other arcuately with respect to the bit axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a longitudinally greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; each of said teeth having its trailing face concave in a direction laterally of the tooth, whereby said leading and trailing faces of each tooth are spaced different distances from each other to'provide a variable tooth thickness laterally of the tooth.

10. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting member; said drag cutter structure including a plurality of depending teeth of extended length spaced from each other arcuately with respect to the bit and axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder in the well bore which opposes the advance of said teeth; at least one of said teeth having an outer longitudinal reaming surface extending radially outward to a longitudinally greater extent than the corresponding outer surface of another of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; at least one tooth having an intermediate groove therein extending upwardly from said lower cutter face; and hardfacing material in said groove secured to said one tooth.

11. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting member; said drag cutter structure having a plurality of depending lateral teeth of extended length in juxtaposition throughout their entire lateral extent and spaced from each other arcuately with respect to the bit axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the ad- Vance of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; at least one tooth having one of its faces concave in a direction laterally of said one tooth, whereby said one face is spaced ditferentdistances from said other face of said one tooth to plfovide a variable tooth thickness laterally of said toot 12. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting member; said dragcutter structure having a plurality of depending lateral teeth of extended length in juxtaposition throughout their entire lateral extent and spaced from each other arcuately with respect to the bit axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; each of said teeth having one of its faces concave in a direction laterally of the tooth, whereby said one face is spaced different distances from the other face of the same tooth to provide a variable tooth thickness laterally of the tooth.

13. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting memher; said drag cutter structure having a plurality of depending lateral teeth of extended length in juxtaposition throughout their entire lateral extent and spaced from each other arcuately with respect to the bit axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; each of said teeth having its leading face concave in a direction laterally of the tooth, whereby said leading and trailing faces of each tooth are spaced diiferent disstances from each other to provide a variable tooth thickness laterally of the tooth.

14. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting member; said drag cutter structure having a plurality of depending lateral teeth of extended length in juxtaposition throughout their entire lateral extent and spaced from each other arcuately with respect to the bit axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; each of said teeth having its trailing face concave in a direction laterally of the tooth, whereby said leading and trailing faces of each tooth are spaced different distances from each other to provide a variable tooth thickness laterally of the tooth.

15. In cutter means adapted to be mounted on the main body of a rotary drill bit to be lowered in a well bore: a supporting member having means thereon for mounting said member on the main body; an integral drag cutter structure secured to said supporting member; said drag cutter structure having a plurality of depending lateral teeth of extended length in juxtaposition throughout their entire lateral extent and spaced from each other arcuately with respect to the bit axis and throughout their length to provide a space between adjacent teeth throughout the length of said teeth and having their lower cutter faces lying in the same plane so that all teeth and lower faces are adapted for simultaneous operation upon a shoulder formed in the well bore which opposes the advance of said teeth; each of said teeth having a leading and a trailing face; hardfacing material on said leading faces substantially throughout their length; at least one tooth having an intermediate groove therein extending from its leading to its trailing faces and upwardly from its lower cutter face; and hardfacing material in said groove secured to said one tooth.

References Cited in the file of this patent UNITED STATES PATENTS 1,776,018 Brown Sept. 16, 1930 1,809,351 Oliver June 9, 1931 1,851,261 Pechacek Mar. 29, 1932 1,899,771 Reed Feb. 28, 1933 1,913,550 Holt et a1. June 13, 1933 1,923,487 Howard et a1. Aug. 22, 1933 1,949,591 Vaughn Mar. 6, 1934 1,983,488 Pedigo Dec. 4, 1934 2,090,058 Mangels Aug. 17, 1937 2,190,434 Pivoto Feb. 13, 1940 2,506,341 Bullock May 2, 1950 2,740,651 Ortlofi Apr. 3, 1956 2,758,819 Kammerer Aug. 14, 1956 FOREIGN PATENTS 612,147 Germany Apr. 13, 1935 

